Most automobiles and trucks (herein vehicles) include a lock positioned at or near a door to prevent unauthorized entry into the riding compartment of the vehicle. The lock is typically positioned on the exterior frame of the vehicle for access by the operator of the vehicle. A key is usually provided for engaging a cylinder for unlocking the lock. The door may also include a latch and a handle so that, once unlocked, the handle may be used to unlatch the door and permit opening of the door for entry into the riding compartment of the vehicle.
During freezing weather conditions such as snow, freezing rain, or ice, the lock cylinder may become frozen, thereby prohibiting the operator from unlocking the lock to gain entry to the vehicle. To enable the operator to gain access to the vehicle, prior art devices have been proposed for heating the lock thereby to melt the ice and permit engagement of the lock with the key. These devices typically provide a heating element that is positioned proximate the cylinder for heating the cylinder to remove any ice that has accumulated therein, so that the key may be engaged with the cylinder to unlock the lock. However, these prior art devices include controls for energizing the heating element that suffers from one or more of the following disadvantages.
Some prior art controls for energizing the heating element include devices that activate the heating element immediately upon movement of the door handle in a predetermined position (referred to as the deicing position). These devices require that the door handle be positionable in at least three positions, i.e., the normal position, the unlatching position, and the deicing position. However, providing a door handle that is movable in at least three positions is costly and therefore undesirable. When this energizing circuitry is used with a door handle that is movable in only two positions, i.e., the normal position and the unlatching position, so that the unlatching position is the deicing position, then the heating element is activated each time the door is opened thereby causing unnecessary waste of energy and, accordingly, being undesirable.
Other prior art devices disclose an external switch, positioned on the exterior of the vehicle, for activating the heating element. However, these devices require the external switch to be bulky and cumbersome so that it does not freeze. Accordingly, these devices are not effective when used with small switches and are expensive when used with switches that will not freeze. Still another device provides exterior contacts that the operator is to bridge using a conductive element to activate the heating element. These devices, in addition to being cumbersome to use, are somewhat dangerous in that the operator may be exposed to a potential difference between the exterior conductors and ground. Accordingly, it is desirable to provide a heating element for a lock cylinder of a vehicle that may be energized using a simple and inexpensive method and apparatus.
Still further, prior art devices for activating a heating element fail to provide an effective method or apparatus for terminating energy to the heating element after a time has elapsed to allow deicing. As an example, one prior art device enables the heating element to be activated so long as the door handle is in a predetermined position. This device requires the operator to continually monitor the lock cylinder to determine when the cylinder has adequately deiced. Accordingly, it is desirable to provide a method and apparatus for energizing a heating element for a lock cylinder and for terminating battery energy to the heating element after sufficient time has elapsed for deicing.